[Topfun99]

The valve head likely broke off first, otherwise the many marks on the top of the pistons would not be there - the piston was pounding the valve head into the chamber over a number of engine revolutions.
The valve being incompressible is likely what cause the rod to buckle, and once it was folded up, the crank beats the bottom of the piston, then, after the rod breaks completely into 2 pieces, the remaining part of the big end which is still attached to the crank, also beats the bottom of the piston.

My opinion is that the valve failed first - look for the cause of that. - possibly the guide was sticking causing piston to valve contact, or the valve overheated and the material failed ....


MANY - approximately like trying to compress a stainless steel valve head

If you read my analysis, the piston DID NOT STOP after the rod broke. The broken part of the big end kept hitting it from underneath and the boost pressure coming thru the intake side (and also to a lesser extent the back pressure from the turbo on the exhaust side) kept pushing it down towards the bottom of the cylinder. So the piston was bobbing up and down for quite a bit. That accounts for the multiple hits on the intake valve. The failure occurred around 6600 rpm and it was between 5-10 seconds before it stopped turning.

For those who think the piston stopped, here is a picture of EXACTLY where the piston was in the cylinder when I took the head off. It was nowhere near the top so something kept pushing it down and eventually the big end of the rod was too short to push it back up anymore.

 

[Topfun99]

You obviously have not seen many catastrophic engine failures. This is textbook dropped valve damage on top of the piston. How on earth do you think the valve is going to hit the piston and combustion chamber dozens of times and hard enough to leave dents with a broken connecting rod? That is purely nonsensical.

Your reading comprehension is horrible. I explained very clearly how/why that piston kept moving.

If you want to point out the problem with my explanation, feel free. But I am tired of reading your "no it didn't" without any discussion of why my analysis is incorrect.

 

[DeepBrainThrombosis]

Yea I agree with Randy. If the valve did break off first there would be a huge hit from the valve in your combustion chamber. Your chamber and top of piston only have light hits in it. I would think to break a rod in compression the valve would be imbedded into the piston like .5inch deep.

Here’s an experiment for you. Grab a scrap forged piston, mount it in a vice, and hit it with a hammer. See how much force it requires to make a dent “a half inch deep”.

Aluminum is softer than steel, but some of you seem to think it’s soft like lead apparently.

You seem to forget, with the valve head broken off, the piston will only squeeze it into the head at near the top of the cylinder, where piston speed has slowed down substantially.. the actual pinch point might only be a handful of degrees of crankshaft rotation on each pass. We’re not talking about the piston encountering pushback halfway down the cylinder when piston speed is at it’s fastest. It’s right near the top, and just for a handful of degrees of crankshaft rotation.. but it’s still a lot of stress on the rod, that is cumulative over dozens of such passes.. each hit stresses the rod and pushes it that much closer to failure. You’re thinking in terms of the rod failing the first time it hits the valve. You should be thinking about the fact that it was probably stressed over 50+ cycles of pinching that valve between piston and head. Each cycle it got weaker, until it failed.

Think about the opposite scenario - rod breaks first, piston is now free to move.. do you actually, really believe the rod flailing around is going to drive that piston all the way up to the top of the cylinder with enough force to not only just happen to time it perfectly to hit ONLY the open intake valve and NOT the exhaust, but do it enough times to break off the valve? The piston was forced back up the cylinder by the flailing rod and just happened to hit the intake valve ONLY at just the right time, multiple times to break the valve off, then continued to travel up and down the cylinder 50+ more times with enough force to create dents? That’s an absurdly unrealistic scenario that is simply not believable.

 

[DeepBrainThrombosis]

If you read my analysis, the piston DID NOT STOP after the rod broke. The broken part of the big end kept hitting it from underneath and the boost pressure coming thru the intake side (and also to a lesser extent the back pressure from the turbo on the exhaust side) kept pushing it down towards the bottom of the cylinder. So the piston was bobbing up and down for quite a bit. That accounts for the multiple hits on the intake valve. The failure occurred around 6600 rpm and it was between 5-10 seconds before it stopped turning.

For those who think the piston stopped, here is a picture of EXACTLY where the piston was in the cylinder when I took the head off. It was nowhere near the top so something kept pushing it down and eventually the big end of the rod was too short to push it back up anymore. View attachment 717590

Did you come here to argue, or to actually try to figure out what happened? The majority of the people who have commented disagree with you. What do you have to gain by arguing with the people who are trying to help analyze your failure?

 

[turbobug64]

There are like maybe 20-30 hit marks. If the valve broke at say 7000RPM then the piston is moving up and down. 116 times per second. Your theory doesn't add up. Plus the top of that piston has barely any damage. I have ran pistons with more damage. That is not anywhere near the damage you see when a valve head comes off.

 

[DeepBrainThrombosis]

Your reading comprehension is horrible. I explained very clearly how/why that piston kept moving.

If you want to point out the problem with my explanation, feel free. But I am tired of reading your "no it didn't" without any discussion of why my analysis is incorrect.

Your explanation is absurd, as I very clearly stated.

Here’s another experiment for you: Thread a fitting into the spark plug hole and hook an air hose up to that cylinder and apply 23psi to it.. now, hit that piston from the bottom with a hammer and see if you can drive it all the way up the cylinder with enough force to make dents in it. I bet you can’t do it even without the air pressure in the cylinder. I don’t think you understand how much force is required to make those dents. You think the swinging loose connecting rod end smacking the piston - at just the perfect timing, mind you - is imparting enough force to drive the piston up the cylinder with enough force against 23 psi boost to break off a valve head, then keep doing it 50+ more times? With the piston just perfectly timing it’s downstroke to meet up with the crank pin and/or loose rod at just the right moment to receive another smack to drive it back up? The absolutely perfect timing required on 50+ consecutive cycles is so laughably impossible, I can’t believe anyone would actually think that’s a more likely scenario that a valve snapping, which happens ALL the time.

 

[schick]

After looking at the pictures again this morning. The piston head does not have the damage i thought it did. When I first looked at the picture, I thought there was holes through the piston. I beleive the rod broke first (changing my previous opinion). The boost pressure held the broken rod and the piston together (hence the minimal damage and witness marks), the centrifugal force of the broken rod pushed the piston into the valve brakeing it. That cylinder is now a pneumatic piston being pushed up with the remnants of the rod and back down with boost pressure every crank revolution, not following the cam events.
The question about the force to compression break that rod? Would not guess a number, but it would be large. I think that is plausible but unlikely. Rods do fail on the compression stroke as you know.
How many passes on those rods?

be safe, schick

 

[Topfun99]

After looking at the pictures again this morning. The piston head does not have the damage i thought it did. When I first looked at the picture, I thought there was holes through the piston. I beleive the rod broke first (changing my previous opinion). The boost pressure held the broken rod and the piston together (hence the minimal damage and witness marks), the centrifugal force of the broken rod pushed the piston into the valve brakeing it. That cylinder is now a pneumatic piston being pushed up with the remnants of the rod and back down with boost pressure every crank revolution, not following the cam events.
The question about the force to compression break that rod? Would not guess a number, but it would be large. I think that is plausible but unlikely. Rods do fail on the compression stroke as you know.
How many passes on those rods?

be safe, schick

480 runs and 30k street miles. I was running those rods right at their HP rating - 1300hp.

When we discussed this with Callies while inquiring about their rods (1500hp rating), they were surprised they lasted 480 runs. So in the future I will have to be more conservative on the number of runs at this level even with their rods.

 

[Topfun99]

Your explanation is absurd, as I very clearly stated.

Here’s another experiment for you: Thread a fitting into the spark plug hole and hook an air hose up to that cylinder and apply 23psi to it.. now, hit that piston from the bottom with a hammer and see if you can drive it all the way up the cylinder with enough force to make dents in it. I bet you can’t do it even without the air pressure in the cylinder. I don’t think you understand how much force is required to make those dents. You think the swinging loose connecting rod end smacking the piston - at just the perfect timing, mind you - is imparting enough force to drive the piston up the cylinder with enough force against 23 psi boost to break off a valve head, then keep doing it 50+ more times? With the piston just perfectly timing it’s downstroke to meet up with the crank pin and/or loose rod at just the right moment to receive another smack to drive it back up? The absolutely perfect timing required on 50+ consecutive cycles is so laughably impossible, I can’t believe anyone would actually think that’s a more likely scenario that a valve snapping, which happens ALL the time.

The rod was beating the bottom of the piston hard enough that eventually both spiral locks on one side came out. That's what drove the piston back up repeatedly. And it DID hit the exhaust valve. The exhaust valve is bent and maybe 1/8" of the seat. It just happened that the intake valve failed first because, even though they have the same stem diameter, the larger intake head produced more sideload on the stem. And the break on the stem was not from elongation failure, it was fractured.

There aren't that many hits on the piston and hardly any in the combustion chamber so yes, it is reasonable that the failure happening at 6800rpm and an engine that kept running for at least 5 second would let the piston go up/down enough to leave the marks that are there.

Note: An engine running 1450deg F EGT temperature with a turbo is going to heat up the top of the piston. At that elevated temperature the aluminum is a lot softer than what you would have at room temperature.

 

[Traction Jackson]

Where those Oliver Speedway rods?

 

[TheBac]

IMO, Randy's thought that the rod broke at the small end first is probably the most plausible. The valve probably broke from the piston stalling at the top of the cylinder after the rod broke, hitting the opening intake valve, causing it to break. After looking at all the pics, there's just not enough damage to the top of the piston, compression chamber or cylinder walls to make me think the valve broke first, not like the extensive damage under the piston.

 

[Pro Stock John]

So Callies is saying that was a lot of runs on the rods, what were they suggesting in terms of capping the runs?

 

[DeepBrainThrombosis]

How then do you explain dozens of distinct hard hits on the piston and combustion chamber that could only be caused by the broken valve being pinched between the two dozens of times? Look closely and you can see clearly just from the pictures that some of the marks obviously line up. A close up analysis in person would surely make it even more obvious. That doesn’t happen dozens of times without the piston going up and down dozens of times with the broken valve bouncing around loose inside the cylinder as the piston repeatedly goes up and down.

You can see the very obvious witness marks from piston to valve contact on other cylinders, yet there are NO such marks in the valve reliefs on the piston that actually broke the valve. Ask yourself, if the piston hit the valve hard enough to break it, why didn’t it even disturb the carbon, let alone leave big divots like we see on other pistons?

It is impossible to conclude that the rod broke first. Simply impossible. NO piston to valve contact in the intake valve relief on the cylinder that dropped the valve. Look at it with your own eyes. The damage on the piston is everywhere but where you’d expect to see it.

 

[Ls3fox]

I kindve feel the rod broke first and that's why it didn't beat the valve into the head, by that I mean the valve is still round and not smashed and stuck in the head like I see with most other valve problems

Either way sorry it let go but it was good to see you at drag week especially after having your hips done good luck with getting it all back together

 

[Topfun99]

IMO, Randy's thought that the rod broke at the small end first is probably the most plausible. The valve probably broke from the piston stalling at the top of the cylinder after the rod broke, hitting the opening intake valve, causing it to break. After looking at all the pics, there's just not enough damage to the top of the piston, compression chamber or cylinder walls to make me think the valve broke first, not like the extensive damage under the piston.

They are called "Ford Small Block Standard Light 302 Windsor".
5.400 length and rated to 1300hp.

Ford Small Block Standard Light 302 Windsor | Oliver Racing Parts

oliverracingparts.com

 

[Topfun99]

So Callies is saying that was a lot of runs on the rods, what were they suggesting in terms of capping the runs?

Didn't get that specific in the conversation but they suggested at the power level I run the rods should be inspected at more frequent intervals including checking for change in length. Honestly, without a very precise jig I don't know how someone could check for a "change in length".

 

[TheBac]

They are called "Ford Small Block Standard Light 302 Windsor".
5.400 length and rated to 1300hp.

Ford Small Block Standard Light 302 Windsor | Oliver Racing Parts

oliverracingparts.com

You know far more than I would ever know, Randy. Thats just my guess what happened. Many, many props to what you've accomplished. Good luck on the rebuild.
I broke a 351C valve years ago., it embedded in the piston and destroyed the head.

 

[Topfun99]

How then do you explain dozens of distinct hard hits on the piston and combustion chamber that could only be caused by the broken valve being pinched between the two dozens of times? Look closely and you can see clearly just from the pictures that some of the marks obviously line up. A close up analysis in person would surely make it even more obvious. That doesn’t happen dozens of times without the piston going up and down dozens of times with the broken valve bouncing around loose inside the cylinder as the piston repeatedly goes up and down.

You can see the very obvious witness marks from piston to valve contact on other cylinders, yet there are NO such marks in the valve reliefs on the piston that actually broke the valve. Ask yourself, if the piston hit the valve hard enough to break it, why didn’t it even disturb the carbon, let alone leave big divots like we see on other pistons?

It is impossible to conclude that the rod broke first. Simply impossible. NO piston to valve contact in the intake valve relief on the cylinder that dropped the valve. Look at it with your own eyes. The damage on the piston is everywhere but where you’d expect to see it.

View attachment 717621

I thought it was quite clear in my explanation that the piston WAS going up and down many times before it finally stopped. If you look at the picture below, the side of the relief has a couple of hard hits from the valve. I took the head of the valve, placed it in the relief and it matched those marks. I'm sure what happened was after the rod broke, the piston was pushed up but was either cocked in the bore or could rock enough enough for the head of the valve to hit the side of the relief where those witness marks are. After the rod first broke and the camshaft was still turning, the piston being driven up into both the exhaust and the intake valves while the were open. The exhaust valve WAS hit (it's bent) but there is NO witness mark on either valve relief because the piston wasn't hitting with the same force it hits if the rod was intact. The force of the piston coming up after the rod broke was still enough to break the intake valve (without a doubt it hit the valve several times) and bend the exhaust valve.

The engine was turning at 6500rpm when the failure occurred. That means in 1 second the crank made 108 revolutions and drove the big end of the rod up into the piston each time until enough of the rod's big end broke off and could no longer reach the piston. That 's why the piston ended up down in the cylinder. It kept getting pushed down and pushed up until the big end stopped hitting it.

Once the camshaft stopped turning, the other valves that hit the other pistons were hit by a piston still being driven by their intact rod. So yes, they had very distinct witness marks that actually dug into the piston material. But being attached to a still intact rod, the forces were much higher than the "loose" piston being thrown up into the open valves and the piston could cock/rock in the bore.

If this doesn't explain it clearly to you than nothing will.

And despite your claim, it is possible to conclude the rod broke first. ALL of the damage follows the scenario explained in my analysis.

 

[Topfun99]

You know far more than I would ever know, Randy. Thats just my guess what happened. Many, many props to what you've accomplished. Good luck on the rebuild.
I broke a 351C valve years ago., it embedded in the piston and destroyed the head.

Yes, a broken valve being hit by a piston attached to an intact rod would be VERY dramatically different.

 

[underpsi68]

They are called "Ford Small Block Standard Light 302 Windsor".
5.400 length and rated to 1300hp.

Ford Small Block Standard Light 302 Windsor | Oliver Racing Parts

oliverracingparts.com

Randy where did you see those rods are rated for 1300hp?

I was told 1000hp from Oliver the couple of times I asked them over the years. I think they are being conservative at that rating.

I run the same rods in my sbf, which is very similar to your setup. Every time I had my engine apart, I install new rod bolts just for piece of mind. One of the machine shops I had do machine work for me a few years back said i couldn't break the rods. I don't think some people realize how much hp these combos can make. I will be watching this thread too see if the cause is figured out. Good luck.